The requested URL could not be retrieved
While trying to retrieve the URL: http://www1.ghost-bikes.dp.ua/?
The following error was encountered:
Unable to determine IP address from host name for www1.ghost-bikes.dp.ua
The dnsserver returned:
Name Error: The domain name does not exist.
This means that:
The cache was not able to resolve the hostname presented in the URL.
Check if the address is correct.
Your cache administrator is support.
Generated Wed, 21 Nov 2012 09:57:05 GMT by none (squid/3.0.STABLE20)

The admin area (/wp-admin) opens as usually and works.
I suppose it is a kind of virus. What should I do?

The domain name does not exist. that seems to be your issue, and it looks the same way from here. Are you sure www1 is correct? What URL are you using to open the admin area?
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Pekka 웃Nov 21 '12 at 10:05

In this case, what could happen that everything worked earlier with this code and just today this error occured?
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Taras PasichnykNov 21 '12 at 12:11

I guess that before that the domain was actually working properly(if you try going to jqueryc.com , you'll see that the domain is now parked - it displays a pre-defined template with adverts and stuff, instead of the normal website). So maybe it wasn't really that malicious - maybe it did just render jQuery, but that is totally not the way to render jQuery - you are not supposed to render jQuery from a non-official 3-rd party site, considering that 1) you have jQuery shipped with WordPress 2) you can use 3 official CDN's(Google's, Microsoft's and Media Temple's) to get jQuery
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Nikola Ivanov NikolovNov 21 '12 at 12:46

If your issue is now fixed, please mark the answer as accepted, so that this question won't stay in the "Unanswered" section any more.
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Nikola Ivanov NikolovNov 21 '12 at 12:47

That's not the problem :) The problem occurs when you try to load the main domain ghost-bikes.dp.ua and not the www1 sub-domain(which obviously is not configured). The problem is a malicious script in functions.php, that inserts HTML from another domain, which then tries to redirect the page, but creates either a redirect loop, or just points to a wrong domain.
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Nikola Ivanov NikolovNov 21 '12 at 10:35